In this study, multi-element doped carbon dots (DXM-CDs) were synthesized via a one-step hydrothermal method, utilizing dexamethasone sodium phosphate (DXM) injection as a precursor. The synthesized DXM-CDs exhibited ultraviolet fluorescence emission at 380 nm, with a fluorescence quantum yield (QY) of 19.7%. The fluorescence intensity of DXM-CDs was quenched via oxidative degradation using KBrO in HPO medium. The presence of Ir ion catalyzed the oxidation of DXM-CDs using KBrO, resulting in an accelerated fluorescence quenching. Based on this catalytic oxidation reaction, a kinetic fluorimetric method for the quantification of Ir ions was developed. The optimum conditions obtained are 0.4 M HPO, 2.0 mg mL of DXM-CDs, 1.0 mM KBrO, reaction temperature of 100 °C, and reaction time of 20 min. Under optimized conditions, the method achieved a detection limit (3σ) of 14 pg mL and linear response was observed in the concentration range of 0.2 to 20 ng mL. The developed method was successfully applied to the determination of Ir ions in water samples, yielding accurate and precise results.